1. Field of the Invention
This invention relates to trajectory planning. More specifically, this invention relates to trajectory planning for a lithography system.
2. Background Art
Many industrial processes involve motion along trajectories that are defined by precise positions at specific times. Photolithography is an example of such a process. In a photolithography process, an illumination source projects an illumination beam. The beam passes through, or is reflected off, a reticle to enable the transfer of a reticle image from the reticle to a substrate, such as a semiconductor wafer.
Scanning techniques are employed in photolithography processes to project a reticle image onto a substrate. These scanning techniques involve moving a reticle across an illumination slot to allow the reticle image to be exposed onto a substrate that is simultaneously moving. Reticles and substrates are disposed on stages that are capable of motion in one or more dimensions.
Long scanning times amount to greater manufacturing costs and less throughput. Therefore, it is desirable to reduce scanning times. In order to decrease the amount of time it takes to execute a trajectory, i.e, execution time, these systems aim to calculate optimal trajectories, i.e, trajectories requiring the least amount of time to execute. The calculation of an optimal continuous trajectory is well known in mathematics. However, a typical lithography system operates in discrete time, not continuous time. That is, a typical lithography system can only receive, process and react to commands in increments of time since the sampling rate of the command and control systems is limited. Further, a typical lithography system is restricted by maximum velocity and maximum acceleration constraints.
Accordingly, what is needed is a system and method for calculating optimal discrete time trajectories for a lithography system.
The present invention relates to a lithography system and method for calculating an optimal discrete time trajectory.
In an embodiment of the present invention, a trajectory planner of the lithography system calculates an optimal discrete time trajectory subject to maximum velocity and maximum acceleration constraints. The trajectory planner begins by calculating a continuous time, three-segment trajectory for a movable device, including a first phase for acceleration at the maximum acceleration to the maximum velocity, a second phase for travel at the maximum velocity and a third phase for deceleration at the negative maximum acceleration to a final velocity. The movable device can be a wafer stage, a reticle stage or a framing blade. Next, the trajectory planner converts said continuous time, three-segment trajectory to a discrete time trajectory. The time of execution of the resulting trajectory is at most three quanta greater than the time of execution of said continuous time, three-segment trajectory.
The present invention reduces scanning times in a lithography system. This advantage increases throughput for a lithography system and reduces manufacturing costs.
Further features and advantages of the invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.